Green Tea is a very popular drink not only in Asian countries but throughout the world.  In western nations, black tea is probably even more popular.

Green tea itself has many potential health benefits including promoting weight loss as well as beneficial effects on glucose tolerance (potentially beneficial for people with diabetes).  Both green, as well as black teas, are rich in polyphenols which are antioxidants.

Despite the many potential health benefits of both green and black teas, a recent study suggests that there may be one important adverse health-related effect related to tea consumption.

Folic Acid:

Folic acid is an important vitamin for several reasons.  Deficiencies of folic acid have been linked to the following conditions:

• cardiovascular disease
• growth retardation
• megaloblastic anemia
• neural tube defects (in children born from mother’s who have deficiency during pregnancy)
• depression
• increased levels of homocysteine

A recent study published in the journal, Biopharmaceutics & Drug disposition (Alemdaroglu et al, 2008), suggests that drinking either green or black tea may actually lower the bioavailability of folic acid.

Study Results:

At the 0.4 mg folic acid dose, green and black tea reduced the mean C(max) of serum folate by 39.2% and 38.6%

Study conclusion:

The present results suggest an in vivo interaction between tea and folic acid with even low concentrations of green and black tea extracts yielding decreased bioavailabilities of folic acid.

Important Implications:

• Pregnant women may want to eliminate or at least restrict their consumption of both green/black tea.  Lower folic acid bioavailability is a potential risk for neural tube defects.
• For those who do consume green/black teas, you will want to ensure that you don’t take your vitamins (containing folic acid) with tea.

Update 2019:

A new research study published in the journal of Epidemiology concluded:

Considering the negative associations of caffeine and tannin levels with serum folate levels, pregnant women should consume caffeinated beverages, such as coffee and green/oolong teas, with caution.

References:

1. Alemdaroglu NC, Dietz U, Wolffram S, Spahn-Langguth H, Langguth P. Influence of green and black tea on folic acid pharmacokinetics in healthy volunteers: potential risk of diminished folic acid bioavailability. Biopharm Drug Dispos. 2008 Sep;29(6):335-48.
2. Otake M¹, Sakurai K¹, Watanabe M¹, Mori C^1,2.Association Between Serum Folate Levels and Caffeinated Beverage Consumption in Pregnant Women in Chiba: The Japan Environment and Children’s Study. J Epidemiol. 2018 Oct 5;28(10):414-419. doi: 10.2188/jea.JE20170019. Epub 2018 Apr 28.